Glow cathode



Feb. 14, 1939. H. KOLLIGS 2,147,447

GLOW CATHODE Filed June 26, 1937 WITNESSES: INVENTOR W Hans f0///y5. z BY W W fi TORNEY- Patented Feb. 14, 1939 UNITED STATES PATENT OFFICE GLOW CATHODE Application June 26,1937, Serial No. 150,520 In Germany September 21, 1936 6 Claims.

My invention relates to cathodes and especially to cathodes for gas or vapor filled discharge devices.

An object of my invention is to provide a cathode having a surface whereby no active material is sputtered therefrom and deposited on the other electrodes to give rise to backfire.

Another objectof the invention is to make the surface of the cathode of such high heat conductivity that there will be little or no danger of local over-heating and the ignition of local spots on the cathode surface.

Other objects and advantages of the invention will be apparent from the following description and drawing, in which the single figure is. a crosssectional view through acathode constructed according to the invention.

One .of the difiiculties with the cathodes of the prior art, which were constructed of a material which emits electrons very copiously, is that particles of the material are apt to be sputtered or otherwise separated from the cathode body and deposited on the other electrodes such as anodes and auxiliary and control grids, and cause backfire. Another difiiculty has been that this type of cathode is somethimes subject to local heating and the local spot thus overheated breaks out into a flame with the consequent damage to the oathode. Furthermore, where such a type of cathode is utilized in gas or vapor filled devices, such as rectifiers and discharge devices, the positive ion bombardment from the gaseous medium sometimes damages the cathode material.

My invention is designed to overcome these disadvantages of the prior art, and in its specific form my invention contemplates enclosing the electron emitting material in a metal framework and providing a porous sintered material in the openings of the metal framework for the passage of the electrons therethrough. In the drawing, the preferred type of cathode is illustrated in which the numeral l identifies the metal framework having openings 2 therein. This metal framework I may consist of a perforated metal tube having these openings 2 or may be a wire in the form of a ribbon wound in a spiral. The inner portion 4 is wholly or partially filled with a material of high electron emissivity as, for example, an earth alkaline metal and the openings 2 are closed by a porous layer 3 of a metal produced by sintering.

The material of high electron emissivity may also be placed in a mixture with suitable filling material, for example, with the oxides of the earth alkali metals. It may be produced from these oxides in the very tubes by reduction, for

example, with the aid of added aluminum powder. The metal layer which, according to the invention, closes the openings in the tube is produced by disposing the suitable metal, for example, nickel, copper, iron or other alloys, in the form of a strokable or sprayable paste on the surface of the perforated tube. In this process, the openings of the tubes are automatically filled with the paste. In conjunction with these, the binding material, for example, parafiine oil, is driven ofi by heating and by increasing the temperature, the deposited finely divided metal containing layer is rigidly burned on. The heating is preferably carried out in a vacuum or in an inert atmosphere by conducting a current through the tubes to the extent that the tubes are filled with alkali or earth alkali metals. A portion of these metals are vaporized during the heating and pass out through the pores and openings of the layer to be sintered and fill these openings. If the alkali or the earth alkali metal is produced by reduction, for example, with the aid of magnesium powder or dust, the formation and the emission of the earth alkali metals takes place after the surface in the openings of the tube is covered by the sintered material.

To produce the sintered layer, chips, powder or dust of a suitable material, for example, nickel, copper or iron or alloys of these metals, may be used. These metals may be converted into suitable form in known manner. The production may also start with mixtures of the metals or under certain circumstances also mixtures of the metal with insulating materials such as earth alkali metal, for example, oxide or carbonates. In this manner, a metal skin is permeated with active material. The active metal is then driven from the inside to the outside of this metal skin. Since the surface is practically free of large amounts of oxide, no active metal is splintered or sputtered from the cathode and deposited on the anode giving rise to backfire. In addition, the heat conductivity of the deposited layer is so large that local overheating of the cathode which may give rise to the formation of torches or local ignition is hardly possible.

The metal framework I may be composed of nickel or copper, and the layer 3 may be composed of nickel or copper particles. These particles may under certain circumstances be oxidized on the surface and thereby form a highly emissive film of a good electron emissive metal, for example, barium. The inner portion 4 of the cathode may be filled with a metallic alkali or around the metal 4 so that the'magnetic field about one coil will be neutralized by the magnetic field in the adjacent coil.

This type of cathode may also be utilized as an indirectly heated cathode. A wire filled with the emissive material and provided with holes therein is first formed as desired. The holes are closed by sintering a metal layer as described above and the cathode is activated. The process may also be carried out by starting with a perforated wire, the openings of which have been closed by sintering metal thereon, converting in the proper form and after this carrying out the activation. The cathode body 4 may be heated by an inner heating body aswell as an outer heating body. These heating bodies may themselves be capable of emission and may consist of a tube produced and activated in accordance with the invention. These heating bodies may, for example, form the sides of a polysided pyramid which is mounted in the cylindrical emission body 4.

It will be noted that the electrons from the body 4 of the'drawing will have egress through the porous sintered body 3 and yet there will be no danger of particles of material being sputtered from the main body 4 to impinge upon the other electrodes to provide a danger of backfire.

Furthermore, where a material of good conductivity both as regards electricity and heat, such as the nickel and copper heretofore mentioned, is utilized for the sintered material 3, there is no danger of local heating and ignition of such local spots.

In case it is not While the cathode described is suitable for high vacuum tubes, it is especially adapted for vapor or gas filled tubes because the porous sintered body 3 protects the electron emitting material 4 from damage due to excessive ion bombardment.

While I have disclosed a preferred embodiment of my invention,it is apparent that many changes maybe made in the size, shape, arrangement and selection of materials without departing from the spirit of the invention. AccordinglyJ desire only such limitations on the following claims as is necessitated by the prior art.

I claim as' my invention:

1. A cathode comprising electron emitting material,.a metal framework enclosing said electron emitting material and a sintered material in the openings in said framework adjacent said electron emitting material.

2. A cathode comprising electron emitting material, a metal framework enclosing said electron emitting material and a sintered material in the openings in said framework adjacent said electron emitting material, said metal framework constituting a heater for said electron emitting material.

3. A cathode comprising electron emitting material, a metal framework enclosing said electron emitting material and a sintered material containing metal particles in the openings in said framework adjacent said electron emitting material.

4. A cathode comprising electron emitting material, a metal wire wound around said electron emitting material and a sintered material in the openings of the metal wire.

5. A cathode comprising electron emitting material, a metal wire wound around said electron emitting material and a sintered metal material in the openings of the metal wire.

6. A cathode comprising electron emitting material, a metal Wire wound around said electron emitting material and a sintered material in the openings of the metal wire, said wire constituting a heater for said electron emitting material.

HANS KOLLIGS. 

